1. Field of the Invention
This invention relates generally to antennas, and more particularly to antennas which seek to propagate a radiation pattern omnidirectionally in the azimuth plane and must do so proximate to an obstruction.
2. Description of the Prior Art
In monopole antennas, a conductive radiating element extends out perpendicularly to a ground plane. A generator or other voltage source then applies a voltage between the element and the ground plane. Due to space limitations, equipment must often be located near to the radiating element. An obstruction that is located within 0.05 wavelengths of the radiating element disrupts the propagation of radiation from the radiating element. This disruption of the radiation pattern occurs because the radiating element has more capacity to the obstruction than to free space. This causes a signal equal in magnitude to the signal being radiated from the radiating element to be generated at the obstruction. The signal generated at the obstruction is 180.degree. out of phase to the radiated signal. Thus, the radiated signal is shorted at the monopole base which disrupts the projection of the radiation pattern. Practical space limitations often prevent moving the radiating element to an adequate distance away from the obstruction to prevent disruptive shorting of the signal.